The present invention relates to reflective asphalt emulsions and more particularly to novel method and compositions for producing such reflective emulsions, which may be used advantageously as a roofing and waterproofing composition having superior characteristics.
Prior asphalt emulsion mixtures have been applied to roofs and other substrates, sometimes as a protective coating and sometimes as a re-cover system, using a reinforcing sheet. Such asphalt mixtures have little or no reflectivity in that they are typically black in color. In many circumstances, however, it has been found desirable to use asphalt coatings and sealants for roofing, paving, waterproofing, sealing, etc., with increased reflectivity. This is particularly true where the asphalt is exposed to sunlight and other solar radiations. For example, it has long been known that asphalt roofing installations are subject to moderately severe thermal expansion and contraction cycles as they heat beneath the sun during the day and cool at night. Repeated thermal shock cycles of this type lead to accelerated breakdown of the asphalt and destroy its effectiveness as a roofing, waterproofing, or sealing membrane, and therefore lead to eventual damage to the protected structure due to rain and weather. And while it has long been realized that increasing the reflectivity of such installations would decrease their absorption of solar radiation, and thereby reduce the thermal stresses and shock cycles to which they are subjected--and thus would prolong the life of the installations and of the structures they are intended to protect--no satisfactory means for increasing the reflectivity of asphalt has yet been put forward.
One proposal has involved the use of aluminum coating asphalts. Such asphalts provide a thin aluminum surface coating atop an installed asphalt layer (or membrane) and provide relatively high reflectivity. But while aluminum coating asphalts have been found to be extremely useful and beneficial in many applications, it has also been found that in many other circumstances they are not suitable. For example, the aluminum coating formed in the application of such asphalts is typically extremely thin, and, as the asphalt beneath or behind it hardens, the coating tends to become relatively brittle. In such circumstances relatively light physical impacts can break the coating, and cause flaking and therefore loss of reflectivity and even (when the asphalt beneath it breaks also) loss of moisture resistant integrity. For example, the surface of an installed aluminum coating roofing asphalt for a portion of a roof subjected to foot traffic (as for example for maintenance purposes) tends to break down and lose substantial portions of its reflectivity due to the stresses caused by individuals walking on it, leading to increased thermal shock loadings in the asphalt and eventual failure of the asphalt as a roofing membrane.
Another approach has been the simple painting of asphalt installations, using, for example, light-colored latex paints. But paints used in such installations typically cannot weather the stress of physical impacts, such as the walking previously described, or the ponding of water (as for example during or after rainstorms), and they do not wear well: they tend to both break down structurally and lose reflectivity with age and exposure.
Thus there is a need for a durable, wear-resistant, highly reflective asphalt suitable for use in roofing, waterproofing, and sealing applications, and for application at ambient temperatures.